1. Field of the Invention
The present invention relates to a technique for injecting melt such as a melted plastic into a mold by using an injection machine, and relates in particular to a system for automatically determining the optimum molding conditions necessary to produce molded parts having a required quality.
2. Background Art
In one production method for molded parts, it is necessary to determine optimum molding conditions and to control an injection machine according to the optimum molding conditions thus determined.
Conventional methods for determining such optimum molding conditions, require a skilled-operator to determine the optimum molding condition, drawing upon his experience with respect to injection molding techniques. More specifically, the skilled-operator repeats the production of the molding parts and the evaluation of the produced molding parts modifying the condition of the injection molding machine and determines the optimum molding conditions through trial and error production.
In this method, whether or not preferred optimum molding condition is obtained depends on the skill of the operator who determines the molding conditions. Therefore, an apprenticeship training is very important. However, it is difficult to obtain such skilled operators. Therefore, a system in which an operator can easily obtain the optimum molding conditions, even if he is an amateur with no experience with injection molding, is desired.
On the other hand, a system is used for obtaining a good mold design. In this system, a model is made by a computer based on a form of a molding part to be produced. A plastic flow analysis is then carried out by the computer. In this analysis, the plastic flow under molding conditions which are inputted by an operator is simulated. The design of the molding part is then determined based on the result of the plastic flow analysis.
However, this system has no evaluation means for evaluating the result of the plastic flow analysis and the system provides only the plastic flow analysis result corresponding to the molding conditions inputted by the operator. Therefore, a person who has skill with respect to the injection molding technique should repeat the following steps in order to obtain the optimum molding conditions.
a. Evaluating the result of the plastic flow analysis obtained by the system PA1 b. Modifying the molding condition based on his knowledge referring to the result PA1 c. Inputting the modified molding condition to the system to obtain the next plastic flow analysis and returning to the evaluation of the next result of the analysis (step-a) PA1 a. Instead of the use of the molding condition optimization system described above, the plastic flow analysis is repeatedly carried out by using a flow analysis system, which is a software executed by a computer, under the control of a skilled-operator. PA1 b. An initial molding condition for actual molding and allowable ranges of parameters of the molding condition are determined according to the result of the reported analysis obtained from the flow analysis system and knowledge of the skilled-operator. PA1 c. A test-shot is carried out using an injection molding machine to produce molding parts. PA1 d. An information with respect to the defective molding of the molding parts is inputted to a condition improving system in a computer by a operator so as to obtain an improved molding condition. PA1 e. A test-shot is carried out again based on the improved molding condition. PA1 (1) The system provides only injection conditions as the optimum molding conditions. The optimum clamping side condition is not obtained from the system. Unskilled operators cannot determine the optimum clamping side condition and therefore cannot carry out the injection molding. PA1 (2) The optimum molding condition provided by the system Is obtained based on theory. Therefore, there are a few differences between the optimum molding condition provided by the system and the actual optimum molding condition to be set to the concrete injection molding machine. Thus, the operator should evaluate the effect of the injection molding based on the molding parts produced by the injection molding machine and carry out by his knowledge a modification or transformation on the optimum molding condition provided by the system based on the evaluation in order to obtain an actual optimum molding condition.
That is to say, a skilled-person is necessary in order to obtain the optimum molding conditions using this system.
Recently, a molding condition optimization system is developed in order to overcome the above problem. This system has an evaluation function for evaluating the result of the analysis and a modification function for automatically modifying the molding conditions according to the evaluation, and determines the optimum molding conditions by automatically repeating the calculation based on these functions.
On the other hand, Japanese Patent Second Publication No. Hei 7-20651 discloses an injection molding condition setting system. This system determines the optimum molding condition by executing the following steps.
Not all the operations of this injection molding condition setting system are executed by the computer. The system makes good use of the judgment of the operator, who has some technical skill, in order to judge the result of the flow analysis, and makes good use of the operator'ss Judgment for detecting the defective molding of the molding parts obtained through the test-shot. The remaining operations are automatically executed by the computer. In this manner, the optimum molding condition is obtained by combining human operation and computer operation.
Comparing the two systems described above, it is clearly understood that the molding condition optimization system is superior to the injection molding condition setting system. This is because, the molding condition optimization system does not require the test-shot and the operator's judgment.
However in practice, when an unskilled operator uses the molding condition optimization system, it is impossible to obtain the actual optimum molding conditions and to carry out the injection molding. This is because the molding condition optimization system has the following problems.